ANNAPOLIS -- Slow-moving, nutrient-rich groundwater may frustrate efforts to meet a 2010 deadline for cleaning up the Chesapeake Bay, said the U.S. Geological Survey in a recent study. Maryland and other Chesapeake Bay Program partners have already implemented measures to fulfill bay nutrient- and sediment-reduction commitments by the deadline, said program Assistant Director Mike Burke. But groundwater takes about 10 years to flow into streams and into the bay, delaying visible signs of water quality improvement, said the survey. The study is a "two-edged sword," Burke said. "We know we have some benefits we have not yet seen (but also), it serves as a real spur to act fast." The Environmental Protection Agency named the bay an "impaired water body," mainly due to the crippling effects of an overabundance of nitrogen and phosphorous on the estuary's fragile ecosystem. The nutrients encourage algal blooms, which deplete the bay of oxygen, resulting in the death of underwater grasses, the presence of toxic bacteria and damaged fisheries. Farm runoff is the most obvious source of nutrient pollution, however, groundwater contributes about 48 percent of nitrogen in streams, the report said, making it a crucial conduit for nutrient transport into the estuary. Nitrogen enters groundwater from rainfall, snow melt, and dissolved fertilizers that percolate down through the soil into underground basins. In the mid-1980s, the Chesapeake Bay Program began efforts to reduce bay nutrients, but improvement has been slow. Under a 2000 agreement, Maryland, Virginia, and other bay states committed to voluntary cleanup targets including cutting nitrogen and phosphorous loads by 40 percent from 304 million pounds to 188 million pounds per year. The multi-agency partnership, including the District of Columbia, has already implemented several measures, Burke said, including applying nutrient management practices to about 3 million acres of agricultural land and to 100 sewage treatment facilities.